The aircraft industry has developed a number of airframe components utilizing modern composite materials, for example, carbon fiber reinforced resins. Despite the fact that such materials exhibit outstanding strength to weight characteristics, use thereof has been limited by the difficulty of fastening such materials. Conventional fasteners have proved to be unsatisfactory for several reasons. One characteristic of composite materials is that the material adjacent the periphery of an aperture therein is subject to shattering or cracking when relatively high unit pressure is brought to bear thereagainst. For example, conventional metal rivets often exhibit metal flow incident to the head upsetting operation that induces high unit pressure on the periphery of the rivet hole. Failure of the composite structure under or adjacent the rivet head may not be evident or even immediate. However, subjection of an airframe to the vibratory environment encountered during normal flight conditions or severe loading as is experienced in inclement weather conditions may result in failure of the composite structure.
While plastic rivets or rivets having plastic heads have been utilized heretofore, such rivets generally do not exhibit characteristics suitable for aircraft applications or applications requiring relatively high strength. For example, the patent to Luth U.S. Pat. No. 2,366,274 teaches forming a plastic rivet by the application of heat to mold soften and cure a thermoplastic material. Luth teaches the use of a thermoplastic material that is initially in the form of a powder that is supported within dies in registry with apertures in two parts to be joined. The powdered material is thereafter cured to form a thermoplastic rivet.
Similarly, the patent to Baker U.S. Pat. No. 2,391,938 teaches molding of a plastic rivet about both sides of a workpiece having an aperture therein. A suitable moldable material which may be thermoplastic or thermosetting in nature is induced into a cavity surrounding the aperture in the workpiece and thereafter cured.
It is evident, however, that riveting of composite subassemblies on a production basis does not allow for the utilization of dies placeable on opposite sides of the workpiece to contain and thereafter cure a moldable resin in either liquid or powder form. Moreover, since most aircraft assemblies are relatively large in terms of surface area, it is preferable that rivets utilized to hold, for example, skins to supporting structures, be capable of assembly from only one side of the workpiece. Such rivets are known in the art as "blind" rivets.
Another desirable feature of a an aircraft rivet is that it be capable of installation by relatively small tools that do not exhibit a vibratory interaction with the rivet.